During the manufacturing procedures of semiconductor integrated circuit packages the IC chip, sealed with resin, is typically subjected to a reliability test, called a burn-in test and an electric property test prior to its shipment, in order to identify good products and unsatisfactory products. Input and output characteristics, pulse characteristics, noise leeway and the like of the IC chips are tested in the electric property test. In the burn-in test, the IC packages that have passed the electrical property test are arranged in an oven and made to operate for a certain period of time at a high temperature, such as 125.degree. C., and under a power voltage which is about 20 percent higher than the rated value. Products which fail the burn-in test are discarded as being unsatisfactory, with only IC packages which perform as intended being shipped out as satisfactory products. In recent years, the BGA package, which has a matrix-like or zigzag arrangement of terminal leads comprising ball-shaped solder bodies on the reverse side of the package, has come into wide use as the IC package of the new surface loading type. The BGA package has the advantage of increasing the width of the terminal pitch with small outside dimensions, with the terminal leads being sufficiently robust that they do not deform upon contacting other parts. FIGS. 14-16 show a socket for burn-in tests made according to the prior art used for loading such BGA packages. As shown in FIGS. 14(a), 14(b), FIGS. 15(a) and 15(b), socket 101 has a square base 102 made of resin and a slider 103 for loading the BGA package arranged for movement in the horizontal direction for loading the BGA package (not shown in the drawing) on base 102. A cover 104, made of resin and having an opening therethrough for passage of BGA packages is provided at the top of base 102 vertically movable relative to base 102 by means of compression coil springs 105 disposed at each of the four corners of the base and cover. A hole (not shown in the drawings) corresponding to each terminal lead of the BGA package is formed through slider 103 and base 102. In addition, an electrical contact 106 is arranged to run through the holes of slider 103 and base 102 for the compressive connection of the terminal lead of the BGA package. Each contact 106 is made of an oblong metal member with a pair of arms 106a, 106b provided at one end. Each contact 106 is vertically fixed on base 102 with arms 106a and 106b extending upwardly as shown in FIG. 15(b). With reference to FIG. 14(b), on the other hand, contact 106 is formed with a protrusion, not shown in the drawing, provided on arm 106a of arms 106a and 106b arranged adjacent to each other, and as the protrusion becomes engaged with a groove 103b formed in a partition wall 103a of slider 103, arms 106a and 106b are opened. A slide mechanism for moving slider 103 in parallel with the bottom of base 102 is provided on both sides of slider 103. The slide mechanism comprises a respective lever member 108, approximately in the shape of an L, with a long arm rotatably mounted at each end of a shaft 107 extending along the edge (on the right side edge in FIG. 14(a)) of base 102 and a short arm 108a of lever member 108 rotatably linked to a shaft 109 (see FIGS. 16(a)-16(c)) which engages the edge of slider 103 which is disposed in parallel relation with the top of shaft 107. In addition, a respective lever member 111 is rotatably mounted at each end of a shaft 110 which extends along the other, left, side edge of base 102. The distal tip of lever member 108 is slidably connected to lever member 111 through a slot (not shown) formed in lever 111 intermediate to the ends thereof. When cover 104 is not being depressed, tip 111a of lever member 111 engages protrusion 104a on the top wall of cover 104. A compression coil spring 113 is provided in the vicinity of shaft 107 for placing a bias on slider 103, toward the right as seen in FIG. 14(a).
In a socket 101 made as described above, if cover 104 is pressed down from the position shown in FIG. 15(a), lever members 108 and 111 pivot toward base 102 and, along with movement of lever member 108, shaft 109 engages slider 103 and moves in the X- direction, to the left as seen in the drawing. As a result of this (see FIG. 15(b), arm 106a of each contact 106 is moved and opens by being engaged with groove 103b of partition wall 103a of slider 103. If, in this state, the BGA package is dropped into the holding part 103c of slider 103, each lead terminal of the BGA package enters between arms 106a and 106b of a respective contact 106. When the downward force on cover 104 is removed, lever members 108 and 111 rise and slider 103 returns in the X+ direction due to the bias of compression spring 113 with arms 106a and 106b of each contact 106 being closed with a respective lead terminal of the BGA package sandwiched therebetween. Because of this, it becomes possible to electrically connect each lead terminal of the BGA package to a respective contact 106.
In recent years, a BGA package with a pitch between the solder balls at approximately 0.75 mm has been developed. However, there arise various problems in the burn-in test using the conventional socket 101 as described above on BGA packages having such a small pitch. In the conventional socket 101, the pressure contacts of arms 106a and 106b of contact 106 are offset and not arranged in such a way as to face each other, with a consequence that it is difficult to firmly sandwich the small solder balls by arms 106a and 106b. As a result, it is not possible to satisfactorily guarantee the electrical connection between arms 106a and 106b and the solder balls. Further, where an oxide film has formed on the surfaces of the solder balls of the BGA package the danger of the electrical connection between arms 106a and 106b and the solder balls becoming unsatisfactory is exacerbated. Another problem relates to the connecting or lead portion of contacts 106 in this type of socket which are inserted into holes formed in the circuit substrate, followed by soldering to thereby electrically effect connections with the circuit substrate. In the case of loading a BGA package having such a small pitch as described above, there is a problem in that it is difficult to insert the connecting parts of contacts 106 into the holes of the circuit substrate due to the extremely small size of the pitch between contacts 106 particularly if one or more leads are slightly bent. Another disadvantage relates to the large number of components required for driving the slider, including lever members 108, 111 and shafts 107, 109 and 110 with a result that the construction becomes complicated and the manufacturing costs are adversely affected.